US3624571A

US3624571A - Precision method and means for positioning contact points in miniature electrical relays

Info

Publication number: US3624571A
Application number: US884987A
Authority: US
Inventors: Nathan H Magida
Original assignee: THERMOSEN Inc
Current assignee: THERMOSEN Inc
Priority date: 1969-12-15
Filing date: 1969-12-15
Publication date: 1971-11-30
Anticipated expiration: 1988-11-30

Abstract

A small cylindrical hardened steel drive shaft having knurled serrations formed circumferentially in a continuous band around a central portion is rotatably mounted in bearing recesses formed in a molded plastic base of a miniature relay adjacent and at right angles to a contact pin hole formed in the base. A contact supporting pin inserted through the pin hole is brought into forced engagement with the serrated portion of the drive shaft which, when rotated, forms racklike mating serrations in the engaging surface of the relatively softer contact supporting pin. A wrench-engaging head formed on the external end of the drive shaft enables partial rotation of the drive shaft to impart linear motion of the order of 0.00005 inch, or less, to the contact supporting pin during final assembly of the relay. After all pins have thus been precisely positioned epoxy is applied to the drive shafts and pins to set and seal them in final position.

Description

United States Patent [72] Inventor Nathan H. Magida Westport, Conn.

[21 Appl. No. 884,987

[22] Filed Dec. 15, 1969 [45] Patented Nov. 30, 1971 [73] Assignee Thermosen, Incorporated Stamford, Conn.

[54] PRECISION METHOD AND MEANS FOR POSITIONING CONTACT POINTS IN MINIATURE 2,862,073 ll/l958 Brutscher ZOO/153.16

Primary Examiner-Harold Broome Attorney-Robert A. Buckles ABSTRACT: A small cylindrical harderied steel drive shaft having knurled serrations formed circumferentially in a continuous band around a central portion is rotatably mounted in bearing recesses formed in a molded plastic base of a miniature relay adjacent and at right angles to a contact pin hole formed in the base. A contact supporting pin inserted through the pin hole is brought into forced engagement with the serrated portion of the drive shaft which, when rotated, forms racklike mating serrations in the engaging surface of the relatively softer contact supporting pin. A wrench-engaging head formed on the external end of the drive shaft enables partial rotation of the drive shaft to impart linear motion of the order of 0.00005 inch, or less, to the contact supporting pin during final assembly of the relay. After all pins have thus been precisely positioned epoxy is applied to the drive shafts and pins to set and seal them in final position.

PRECISION METHOD AND MEANS FOR POSITIONING CONTACT POINTS IN MINIATURE ELECTRICAL RELAYS BACKGROUND AND OBJECTS OF THE INVENTION The invention is directed to an improved method of accurately positioning electromagnetic reeds and contact points in miniature electrical relays, and precision adjusting means for this purpose incorporated in such relays during their manufacture. The method and means of this invention represent improved techniques for the assembly of miniature electromagnetic reed relays of the type disclosed in my U. S. Pat. No. 3,425,008 which issued Jan. 28, 1969 and is assigned to the same assignee as the present application.

A major problem in the manufacture of miniature relays of this type is that of precisely positioning the reeds and contacts during assembly, and of holding these parts in the proper relative positions during'the remaining steps of manufacture and during the service life of the device. The objective is to establish relay performance in terms of precisely specified contact operating and release times, sensitivity, and contact gaps, and to maintain that adjustment of the relative positions of the parts through subsequent variations in the ambient positions of the relay, as well as variations in ambient temperature during the remaining stages of manufacture and final use of the relay. For example, these precisely positioned internal elements must be able to withstand moderate ranges of ambient temperature during final. encapsulation in epoxy, and they must also withstand the relatively severe thermal shocks and stresses of being mounted on and soldered to printed circuit cards.

The prior art technique of assembly and adjustment outlined in my above-identified patent involved inserting the contact pins through relatively tight-fitting holes in a molded plastic base, and then pushing them into the desired relative positions by engagement with a precision external fixture, after which epoxies were poured and cured around the pins to hold them in place. This was not an entirely satisfactory procedure because it proved very difficult to maintain these extremely critical adjustments while the epoxy was being cured. It also proved to be very dift'icult to obtain an epoxy resin that would unaided support the pins adequately through the thermal shock of a printed circuit soldering operation. The degree of accuracy required in positioning these contact elements is of the order of less than one ten-thousandth of an inch, i.e., a change of position of one ten-thousandth of an inch is intolerable.

Accordingly it is an object of the invention to solve the problems of accurately adjusting the contact elements of miniature relays during manufacture.

Another object is to provide a method and means for rapidly and precisely positioning such elements to a very close tolerance.

A further object is to provide means for securing and maintaining such precise adjustments in miniature relays.

An overall object is to produce superior miniature reed relays capable of maintaining desired operating characteristics regardless of physical orientation or substantial variations in ambient temperature.

Other objects of the invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the several steps and the relation of one or more of such steps with respect to each of the others, and the apparatus embodying features of construction, combinations of elements and arrangement of parts which are adapted to effect such steps, all as exemplified in the following detailed disclosure, and the scope of the invention will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawing, in which:

FIG. I is a perspective view of a completely assembled relay here shown enlarged to several times actual size,

FIG. 2 is an enlarged cross-sectional view of the relay of the invention taken along the line 2-2 of FIG. 1 and here shown approximately 10 times actual size,

FIG. 3 is an enlarged bottom view of a portion of the relay structure taken along the line 3-3 of FIG. 2,

FIG. 4 is an enlarged view similar to FIG. 3 showing an alternative embodiment of pin engaging drive shaft, and

FIG. 5 is a greatly enlarged portion of FIG. 3 showing the manner in which knurled portions of a drive shaft engage the surface of a contact pin.

BRIEF DESCRIPTION OF THE INVENTION The objects of the invention are generally achieved by incorporating adjustable fixtures into the base of the relay adjacent to and in engagement with each of the relay contact element supporting pins. Each fixture comprises a hardened steel drive shaft having a head portion engageable by an external wrench and a knurled portion engaging the surface of a contact supporting pin. The axis of the drive shaft is at right angles to the axis of the contact supporting pin, whereby rotation of the drive shaft imparts linear motion to the pin causing it to slide in its mounting hole.

DETAILED DESCRIPTION Referring now in greater detail to FIG. I and FIG. 2 of the drawing, a miniature relay manufactured according to the invention and indicated generally at 10 comprises a molded plastic rectangular body or housing portion 11 having a cover member 12 which may be formed of either metal or plastic. A plurality of pin terminals 13-18 in FIG. 1 protrude from the bottom of relay I0 and are adapted for soldering to a printed circuit board. Hexagonal-

headed drive members

19, 20 and 21 are mounted in the bottom of housing 11 in recesses 22, 23 and 24 where they are accessible during assembly with the aid of a suitable wrench.

The internal construction of relay I0 is indicated by the cross-sectional view of FIG. 2 where reference numeral 25 represents the relay operating coil having a magnetic pole piece 26 in proximity to a U-shaped magnetic member 27 which is secured to a flexible nonmagnetic contact reed 28, which in turn is mounted on the upper end of contact pin 16. The upper end of contact pin 14 is bent into a horizontal position as shown at 29 in FIG. 2 and in the preferred embodiment illustrated forms a normally open contact with reed member 28. The upper end 30 of contact pin 15 is bent to the left as shown in FIG. 2 into a substantially horizontal position and forms a normally closed contact with reed 28. To operate the relay 10 low voltage electrical power is applied to the coil 25 through external contact pins 17-18. When coil 25 is thus energized magnetic fiux from pole piece 26 attracts magnetic member 27 thereby flexing reed 28 upwardly as shown in FIG. 2 and causing it to break contact with end 30 and to close contact with end 29. When coil 25 is deenergized the spring tension of reed 28 breaks the contact with end 29 and restores contact with end 30 as shown in FIG..2. The

contact pins

14, 15 and I6, and their

contact members

28, 29 and 30 are preferably formed of a silver magnesium nickel alloy and are gold plated to prevent corrosion and to assure maximum electrical conductivity. As shown in FIG. 2 contact pins l4, l5 and 16 are passed through tightly fitting

holes

31, 32 and 33 in the base of molded plastic housing 11. As shown in FIG. 2 and FIG. 3 a recessed well 34 is formed in the bottom surface of housing 11 surrounding pin 14 and drive member 19. Corresponding

recesses

35 and 36

surround pins

15 and 16, and receive

drive members

20 and 21.

Referring now to FIG. 3 of the drawing, the configuration of the driving member 19 and the manner in which it is journaled in molded plastic member 11 will be described. Driving member 19 is formed with two coaxial smooth

cylindrical portions

36 and 37 which bear upon corresponding semicylindrical bearing surfaces 38 formed in the welled recess 34 of housing 1 1. The external end of driving member 19 is formed into a hexagonal head portion 39 which rests upon an annular shoulder 40 in counterbore recess 22 within the sidewall of housing 11. Between the cylindrical bearing

portions

36 and 37 of drivingmember 19 are a pair of raised annular

knurled sections

41 and 42 accommodated in a deeper well portion 43 of molded recess 34, whereby the driving member 19 may be rotated in its bearing journal without any interference between the raised knurled sections 41-42 and housing 11.

In assembly of the contact pins and adjustable drive means according to the invention, drive member 19 is placed in its semicylindrical bearing cradle 33 within recess 34 and two drops of thermosetting epoxy resin 44 and 45 are applied to the smooth cylindrical bearing

portions

36 and 37 and to the adjacent exterior surface of housing 11. For this purpose I use a high-viscosity low-temperature epoxy which quickly cures at room temperature. When the epoxy dabs 44 and 45 have set, a suitable wrench (not shown) is engaged with the head 39 of member 19 and a slight rotational force is sufficient to break the seal between the

smooth surfaces

36 and 37 of member 19 and the cured epoxy 44 and 45, without affecting the bond between the epoxy and the molded plastic housing 11. The drive member is now rotatably retained within its molded plastic bearing journal. Next the straight end of contact pin 14 is inserted into guide hole 31 from within the main cavity 46 (FIG. 2) of the housing 11, and the pin 14 is forced downwardly through guide hole 31 and past the raised

knurled portions

41 and 42 of rotatable drive member 19. Because the metal alloy of the pin 14 is softer than the hardened steel of drive member 19 the raised serrated portions of

knurled sections

41 and 42 cut into the otherwise cylindrical surface of pin 14 forming corresponding serrations thereon as shown at 48 in FIG. 2. Thus this substantially linear serrated surface 48 of pin 14 becomes in effect a rack engaging corresponding annular serrations 41 of drive member 19, and the two parts are enabled to function cooperatively in much the manner of a rack and pinion. Now when the drive member 19 is rotated in a clockwise direction as viewed in FIG. 2 the contact pin 14 is driven upwardly through the exterior wall of housing 11 to increase the gap between

contact members

28 and 29. Conversely, if drive member 19 is rotated counterclockwise contact pin 14 is moved downwardly to reduce the gap between

contact members

28 and 29.

Because the raised

annular surfaces

41 and 42 of drive 19 are very finely knurled, these surfaces contain a multitude of very sharp hard points which press into the slightly softer contact pin 14 to form an exactly corresponding multitude of toothlike impressions, thereby making possible very fine and precise adjustments of contact position through slight rotational adjustment of exterior drive member 19. Also the forced engagement of contact pin 14 with the serrated surfaces of drive member 19 effects a strong clamping engagement of these two parts within the molded plastic housing 11, thereby maintaining sturdy rigidity of the contact elements during the final stages of relay assembly.

To further enhance rigidity, stability, and linearity of contact pin positioning, I form the contact pin holes through housing 11 with two noncylindrical flat wall portions 50 and 51 angularly disposed opposite to the serrated engaging portion of drive member 19, as is more clearly shown by the greatly enlarged cross-sectional view of FIG. 5. With this construction the force of engagement between contact pin 14 and the raised

serrated portions

41 and 42 of drive member 19 causes elastic deformation of the molded plastic material adjacent surfaces 50 and 51 thereby obtaining a tighter engagement between the contact pin and the housing 11.

FIG. 4 of the drawing discloses an alternative construction of the drive member 19 wherein only a single annular raised collor portion 52 is provided with a serrated surface for cooperative engagement with a contact supporting pin such as 14. While this construction has proven perfectly operable in tests, and is clearly within the scope of the invention, I prefer the dual serrated raised annuli construction of FIG. 3.

For precisely determining the desired positioning of internal contacts such as 29 in FIG. 2, therelay coil 25 is energized with a low-voltage squarewave form signal of predetermined periodicity. The coil energizing signal is also applied to the horizontal sweep circuit of a cathode ray oscilloscope (not shown), and the transfer contact terminals 14, I5 and 16 are connected to the vertical deflection circuit of the oscilloscope. The horizontal trace then appearing on the oscilloscope represents the time duration of the applied square wave pulses, and since this factor has been predetermined the horizontal trace can be accurately calibrated in milliseconds. The operate and release times of the relay transfer contacts appear as vertical deflections on the horizontal trace and are measured by the horizontal displacement therebetween. By slight turning adjustments of a wrench engaging the hexagonal heads of

drive members

19, 20 and 21 while the relay is so connected and operated, the desired optimum operate and release times may be accurately and quickly set. This method of precise adjustment is easily performed by a relatively unskilled operator who may become familiar with the procedure in a matter of minutes, thus enabling rapid and economical precision production of an assembly line basis. When the relays have been so adjusted a low-temperature thermosetting epoxy resin is applied over each drive member and around the base of each externally extending contact pin to substantially fill the

recess wells

34, 35 and 36, thus effectively sealing and locking the pins and drive members in their final positions. Following this operation the contact enclosing chamber 46 (FIG. 2) is evacuated and degased, back filled with an inert gas and sealed, and the relay assembly is completed.

It is to be understood that while the above description has referred in detail to the adjustment of three

contact supporting pins

14, 15 and 16, the present commercial embodiment of the relay 10 includes three corresponding sets of contact pins and drive means (not shown) to form a double-pole-doublethrow Form C relay. Of course the method and means of the invention may be employed in any desired type'of relay, or any other device where rapid and accurate precision adjustments of the relative positions of parts may be required.

For the molded plastic body or housing portion 11 I prefer to use glass-filled, or glass-reinforced, diallyl phthalate, which is a readily available thermal setting material having excellent physical and electrical characteristics. For the contact pin members such as 14, 15 and 16 I use gold-plated silver magnesium nickel alloy. And for the drive members such as 19, 20 and 21 I use a low-carbon screw machine steel stock, such as employed in the manufacture of Allen wrenches. After machining the drive members are case hardened and gold plated to prevent corrosion.

It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are efficiently attained and, since certain changes may be made in carrying out the above method and in the article set forth without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention which, as a matter of language, might be said to fall therebetween.

Having described my invention, what I claim as new and desire to secure by Letters Patent is:

1. In an electromagnetic relay having a magnetic core, an electrically conductive coil surrounding said core, at least one fixed electrical contact, at least one electrically conductive armature movable to and from electrically conductive contacting engagement with said fixed contact, the combination comprising: an insulating external housing, a member slidably inserted through a restricted aperture in said insulating housing and supporting said fixed contact on one end thereof within said housing, a rotatable drive member journaled in said insulating housing adjacent and substantially at right angles to said contact supporting member, and a band of serrated protrusions on said rotatable drive member forcibly engaging with a linear portion of said contact supporting member whereby corresponding serrated indentations are impressed into the linear surface of said contact supporting member upon rotation of said drive member.

2. In an electromagnetic relay having an insulating exterior wall, means for adjustably positioning internal contact members comprising in combination:

A. a plurality of metallic contact supporting pin members, each said member extending through a separate mounting hole in an exterior insulating wall of said relay,

B. a plurality of rotatable hardened metallic driving shafts journaled in recesses in said exterior insulating wall, each said driving shaft adjacent to and in forced engagement with one of said pin members, the rotatable axis of each said driving shaft substantially at right angles to said adjacent pin member, and

C. knurled serrations formed on a portion of each said driving shaft in forced engagement with a linear portion of said adjacent contact supporting pin whereby rotation of said driving shaft impresses corresponding serrations into the linear surface of said adjacent contact supporting pin and imparts linear sliding motion to said adjacent .pin in its mounting hole through said relay wall.

3. The combination of claim 2 and,

D. clamping means applied to said driving shafts and supporting pins to prevent relative motion therebetween after their adjustment to preselected positions.

4. In an electrical relay device means for precisely adjusting the relative positions of a plurality of internal contact members comprising, in combination:'

A. an insulating wall member,

1. a plurality of linear mounting holes through said wall member corresponding to said plurality of contact members,

2. a plurality of recesses formed in said wall member adjacent said mounting holes,

B. a plurality of metallic contact supporting shafts each having a linear portion adapted to fit snugly in said mounting holes,

1. each said shaft extending through a separate one of said mounting holes,

C. a plurality of rotatable hardened metallic drive members each journaled in a separate one of said recesses in said wall member,

l. each said drive member positioned adjacent to and in forced engagement with one of said linear shafts,

2. said drive members each having an axis of rotation substantially at right angles to the axis of said adjacent linear shaft,

3. the portion of each said drive member in engagement with said shafts bearing annular knurled serrations, and

4. an externally accessible tool-engaging head formed on one end of each drive member whereby rotation of said drive members imparts linear motion to the adjacent linear shafts while impressing corresponding serrations into the engaged portion of said shafts.

5. The combination of claim 4 wherein the linear portions of said contact supporting shafts and said mounting holes are substantially cylindrical and of substantially the same diameter.

6. The combination of claim 4 wherein the cross section of said contact supporting shafts is nonconforming to the cross section of said mounting holes and the engagement of said shafts with said mounting holes produces elastic deformation of a portion of said insulating wall member adjacent a portion of said shafts opposite to the portions of said shafts engaged by the knurled serrations of said drive members, whereby a tight force-fitting clamping engagement is maintained between said members.

7. The combination of claim 6 wherein said contact supporting shafts are cylindrical, said mounting holes are approximately cylindrical and of the same diameter as said shafts but said mounting holes are formed with a pair of planar wall portions forming chords of said approximately cylindrical holes,

Claims

2. In an electromagnetic relay having an insulating exterior wall, means for adjustably positioning internal contact members comprising in combination: A. a plurality of metallic contact supporting pin members, each said member extending through a separate mounting hole in an exterior insulating wall of said relay, B. a plurality of rotatable hardened metallic driving shafts journaled in recesses in said exterior insulating wall, each said driving shaft adjacent to and in forced engagement with one of said pin members, the rotatable axis of each said driving shaft substantially at right angles to said adjacent pin member, and C. knurled serrations formed on a portion of each said driving shaft in forced engagement with a linear portion of said adjacent contact supporting pin whereby rotation of said driving shaft impresses corresponding serrations into the linear surface of said adjacent contact supporting pin and imparts linear sliding motion to said adjacent pin in its mounting hole through said relay wall.

2. a plurality of recesses formed in said wall member adjacent said mounting holes, B. a plurality of metallic contact supporting shafts each having a linear portion adapted to fit snugly in said mounting holes,

3. The combination of claim 2 and, D. clamping means applied to said driving shafts and supporting pins to prevent relative motion therebetween after their adjustment to preselected positions.

4. In an electrical relay device means for precisely adjusting the relative positions of a plurality of internal contact members comprising, in combination: A. an insulating wall member,

7. The combination of claim 6 wherein said contact supporting shafts are cylindrical, said mounting holes are approximately cylindrical and of the same diameter as said shafts but said mounting holes are formed with a pair of planar wall portions forming chords of said approximately cylindrical holes, said planar wall portions angularly and oppositely disposed from the portions of said shafts engaged by said drive members, and each of said drive members is provided with a pair of axially separated raised annular knurled portions, whereby the serrations of said drive members forcibly engage said cylindrical shafts at two points opposite said two planar wall surfaces.

8. The combination of claim 4 and, D. clamping means applied to said drive members and said contact supporting shafts to prevent relative motion therebetween after adjustment to preselected positions.